In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower delays and so on (see non-patent literature 1). Successor system of LTE—referred to as “LTE-advanced” (also referred to as “LTE-A”)—have been under study for the purpose of achieving further broadbandization and increased speed beyond LTE, and the specifications thereof have been drafted as LTE Rel. 10 to 12.
The system band in LTE Rel. 10 to 12 includes at least one component carrier (CC), where the LTE system band constitutes one unit. Such bundling of a plurality of CCs into a wide band is referred to as “carrier aggregation” (CA).
In LTE of Rel. 8 to 12, the specifications have been drafted assuming exclusive operations in frequency bands that are licensed to operators—that is, licensed bands. For licensed bands, for example, 800 MHz, 2 GHz and/or 1.7 GHz have been in use.
In LTE of Rel. 13 and later versions, operation in frequency bands where license is not required—that is, unlicensed bands—is also a target of study. For unlicensed band, for example, 2.4 GHz, which is the same as in Wi-Fi, or the 5 GHz band and/or the like may be used. Although carrier aggregation (LAA: license-assisted access) between licensed bands and unlicensed bands is placed under study in Rel. 13 LTE, there is a possibility that, in the future, dual connectivity and unlicensed-band stand-alone will becomes targets of study as well.